As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
External AC-DC adapters or power supplies are commonly employed to convert alternating current (AC) wall current to direct current (DC) for powering DC-powered systems, including DC-powered information handling systems such as notebook computers. Power-factor correction (PFC) control schemes have been developed for AC-DC power supplies to comply with the EN61000-3-2 international standard for limiting harmonic current emissions in input line currents. Among these schemes are active PFC techniques for single-phase boost converters.
Power supplies for relatively low power electronic products that consume less than 250 Watts of power (e.g., such as AC-DC adapters for notebook computers, lighting and LCD monitors, etc.), need additional PFC techniques to maintain low harmonic distortion of the input line current. Typically, continuous conduction-mode (CCM) is not used in such low power electronic products because a relatively large inductor is required to maintain operation in CCM. The critical-conduction-mode (CRM) of operation has several advantages to CCM, such as use of a smaller sized inductor that allows reduced PCB area, decrease of inductor current to zero during turn-off time can result in zero-current-switching (ZCS) to increase efficiency, etc. Thus, CRM has been widely applied for low power electronic products rather than CCM.
Bulk capacitors have been employed with feedback in conventional PFC/PWM stage circuitry of power supplies to maintain a relatively high and substantially constant output voltage (e.g., such as 400 volts DC) to the primary windings of the main transformer of the power supply. FIG. 1 illustrates a DC-powered information handling system 104 (e.g., such as a notebook computer) that is coupled by a DC power connection 130 to conventional AC-DC adapter system 102. AC-DC adapter 102 is configured to receive AC mains power supply 101 and to convert the provided AC power to DC power that is provided to DC-powered information handling system 104 via DC power connection 130. AC-DC adapter 102 of FIG. 1 is configured to be removably and/or temporarily connected to supply DC power across DC power connection 130 to DC-powered information handling system 104 via a removable power plug interconnect 170 that mates with a corresponding power socket interconnect 172 of the DC-powered information handling system 104 that allows repeated coupling and decoupling or physical separation of the interconnects and power connection by a user. In FIG. 1, DC-powered information handling system 104 includes a system load 156 (such as CPU and other processors, display, disk drive/s, wireless communication circuitry, etc.) that is powered by DC power provided through power switching circuitry 154 from AC-DC adapter 102 and/or battery system 152 which is typically a smart battery system. System load 156 of DC-powered information handling system 104 is typically contained within a chassis enclosure, and the circuitry of AC-DC adapter 102 is typically contained within an adapter housing, such as a molded plastic enclosure.
As shown in FIG. 1, AC-DC adapter 102 includes primary mains switcher circuitry 108 and secondary side circuitry 110. Primary mains switcher circuitry 108 is controlled by combination controller 105 (combined PFC and pulse width modulation “PWM” controller) to control supply of AC current from AC mains power supply 101 (e.g., 110/120 or 220/240 AC volts or other AC mains voltage) to primary side of transformer circuitry 112. Transformer circuitry 112 includes primary and secondary side windings that provide voltage isolation between the primary and secondary sides as well as operate to provide a voltage step down (e.g., from 110/200 Volts to 19 Volts or other suitable step down voltage for system 104) for the secondary side power. DC powered information handling system 104 includes power switching circuitry 154 that is coupled as shown to control flow of current between adapter 102, battery 152, and system load 156 of DC-powered information handling system 104. Specifically, power switching circuitry 154 may switch the system load 156 between DC output 130 of AC-DC adapter 102 and battery 152, e.g., according to whether or not DC output power 130 is currently available to power system load 156.
In FIG. 1, AC-DC adapter 102 includes feedback regulator circuitry 118 that is controlled by a controller and that is coupled to receive and monitor DC voltage present on the secondary (DC) side of transformer 112, and to provide an optical switcher control signal 128 across an optocoupler 114 to control operation of primary side switcher circuitry 108 of AC-DC adapter 102. As shown, feedback regulator 118 monitors secondary voltage of DC output 130 from output feedback voltage sense line 122 and sends control signals over optocoupler 114 to the combination controller 105 of primary side switcher circuitry 108 to maintain the DC output 130 in the desired voltage range by using an On/Off signal transmitted to PFC and PWM stage circuitry 103 of primary side switcher circuitry 108 which is duty cycle controlled in such a manner so as to achieve the desired output voltage. In this regard, combination controller 105 is coupled to receive the switcher control signal 128 across the isolation barrier formed by optocoupler 114, and to respond to the switcher control signal by controlling operation of primary switcher side circuitry 108, e.g., by enabling or disabling pulse width modulation (PWM) switching operations of the switcher side circuitry 108 to turn it on or off, respectively.
Also shown in FIG. 1, is power factor correction (PFC) and pulse width modulation (PWM) stage circuitry 103 that is controlled by combination controller 105. PFC/PWM stage circuitry 103 may include inductor, Mosfet and Diode components that are operated to perform the function of power factor correction. PFC/PWM stage circuitry 103 also typically includes a bulk capacitor to maintain a substantially constant output voltage (e.g., about 400 Volts DC) on the high voltage side to the primary windings of the main transformer 112. As shown, controller 105 directly monitors output voltage of PFC/PWM stage circuitry 103 using a first resistive overvoltage protection feedback path (OVP1) 106 that is a voltage divider including four resistors 1-4 that are coupled in series between ground and the bulk capacitor of the PFC/PWM stage circuitry 103, with a feedback voltage detect pin of controller 105 coupled at a measurement node between the first and second resistors from ground to monitor a voltage value or signal indicative of the voltage on the bulk capacitor at the measurement node for comparison to a trigger voltage threshold value. There are two sensing voltage levels of controller 105 (pin connects), for example, 2.5 Volts being general regulation voltage, and 2.75 Volts being the OVP1 trigger voltage threshold level, referring to the divided voltage in voltage divider 106 from the bulk capacitor. Controller 105 only monitors divided voltage and uses a comparator to determine when the divided voltage exceeds the OVP1 trigger voltage threshold.
Combination controller 105 uses this voltage comparison to control output voltage of PFC/PWM stage 105. In this regard, when voltage at the controller feedback voltage pin of controller 105 is detected to exceed the trigger voltage threshold, the combination controller 105 will immediately turn off both PFC/PWM functions of stages 103 to prevent damage to the relatively high voltage PFC bulk capacitor, which may leak electrolyte fluid when damaged. In normal operation, the trigger voltage threshold value for OVP1 shutdown is set lower than the breakdown voltage of the PFC bulk capacitor. When the trigger voltage threshold is exceeded, controller 105 will cause the AC-DC adapter system 102 to shut down and go into latch mode.
When a fault or other problem occurs within the feedback path of OVP1 106 (e.g., such as a short in the feedback path and/or a failure of one or more of the OVP1 resistors due to aging and/or contamination from flux during manufacture), the output voltage of PFC/PWM stage 103 will no longer be controlled since there is no information or incorrect information fed to a feedback pin connection of combination controller 105 through OVP1 106. In this event, combination controller 105 will shut down the PFC/PWM stage 103 and go into protection mode (i.e., shut down mode) to ensure over-voltage protection. A second and redundant resistive overvoltage protection feedback path (OVP2) 111 to allow combination controller 105 to monitor voltage of PFC/PWM stage 103 even when OVP1 fails, e.g., due to component aging or incorrect resistors connected to the feedback detect pin of combination controller 105. OVP2 is also a voltage divider including four resistors 1-4 coupled in series between ground and the bulk capacitor of the PFC/PWM stage circuitry 103 with controller 105 coupled to monitor voltage between the first and second resistors of OVP2 111 in a similar manner as with OVP1. However, inclusion of a second and duplicate OVP2 feedback path 111 acts to increase power consumption due to power loss across the additional resistors of OVP2 111.